1. Field of the Invention
The present invention relates to ink jet printing devices, and more particularly, to a formed orifice plate for use in such devices.
2. Prior Art
Ink jet printing devices basically utilize a liquid reservoir for containing a printing ink and an orifice plate secured to the bottom of the reservoir with a plurality of very small diameter holes fabricated therein constituting orifices. The orifices are often disposed in a row, or a plurality of rows, along the length of a generally rectangular reservoir and orifice plate assembly. In order to control uniformity of drop generation from the plurality of orifices, which is important in order to obtain uniform printing, some means is provided for stimulating vibration of the orifice plate to cause motion of the liquid in a manner which induces pressure waves in the filaments extending from the orifices so that drops of uniform size and spacing are produced from each orifice. Some means is also provided in such devices for selectively catching drops coming from the orifices that are not to be used in printing on a printing medium.
The general construction of such devices is shown, for example, in Sweet et al. U.S. Pat. No. 3,373,437 and in Beam U.S. Pat. No. 3,577,198. There are many alternative constructions for such ink jet printing devices, but many utilize an orifice plate which is formed separately from the manifold forming the ink reservoir with some means being provided to secure the orifice plate and manifold together to prevent leaking.
The main difficulty associated with such constructions is in the various means utilized to secure the orifice plate to the manifold. It is very important to have a uniform contact along the length of the orifice plate between the upper surface of the orifice plate and the bottom contacting surface of the manifold. This is because spurious vibrations are otherwise induced in the liquid in the manifold and thus in the filaments generated from the orifices.
In order to accomplish the most uniform contact, it has been a common practice to either solder or epoxy the orifice plate to the bottom of the manifold. One drawback with epoxying the manifold is the nonuniformity in application of the epoxy which results in distortion of the orifice plate and a variation in the distance of separation between the orifice plate and the manifold. This variation in separation results in spurious vibrations being generated in the orifice plate and the liquid.
With regard to the use of solder, the most serious drawback associated with this technique of applying the orifice plate to the manifold is in the distortion caused by the necessity of heating the orifice plate and the manifold in order to cause adhesion with the solder. Since the orifice plate is relatively thin, it is easily warped when heated causing "row-bow". This phenomenon is merely the distortion of the plate in such a manner that the normally straight row of orifices becomes bowed laterally due to distortion in the plate during heating. This is undesirable since it changes the relative position of the orifices from their otherwise straight line location, causing difficulty with alignment with the charging mechanism and other control features of the ink jet printing device.
Both the use of epoxy and the use of solder to secure a flat orifice plate to the bottom of an ink supply manifold have the additional drawback that they cause contamination of the ink supply since at the joinder line between the orifice plate and the manifold the ink is in contact with either the epoxy or solder.
The device disclosed in the Sweet et al patent, mentioned above, is illustrated as having a slightly different construction which utilizes a unitary orifice plate and manifold construction of rectangular, channel-shaped cross section.
The disclosure of the patent suggests that either the wall containing the orifices or the opposite wall, may be vibrated to induce the proper uniformity in generation of filaments and drops from the orifices. However, it is apparent that spurious vibrations will likewise be induced by either vibrating technique since both the wall containing the orifices and the opposite wall are directly connected to the side walls. Vibrational waves will therefore be induced in the side walls since they are relatively thin, which will cause spurious vibrations in the liquid in contact therewith, thus affecting deletariously the uniformity of generation of filaments and drops from the orifices.
Another problem associated with such prior art devices is that the width of an orifice plate cannot be very wide since interfering vibration is induced widthwise of the orifice plate. The width is therefore generally limited to the wavelength of the first mode of vibration of the highest operating frequency. This then limits the number of rows of orifices which can be included in such an orifice plate because of the necessary spacing between rows required by associated hardware such as drop charging equipment.